I. Field of the Invention
This invention relates to a pattern recognition system, and more particularly to a method and apparatus for more accurately aligning characters before a recognition process.
II. Description of the Prior Art
In pattern recognition systems, if the visual image of the pattern or character being recognized is not properly aligned with respect to recognition apparatus, errors in recognition can occur. The visual image is in the form of a series of resolution elements that are electrical in form. The portion of the scanned area, containing ideally only the pattern to be recognized, is placed within a defined area (referred to as a video space) where it is recognized.
There are many known techniques for aligning the visual image in the video space. Vertical alignment is generally termed registration and horizontal alignment is referred to as segmentation. One alignment method depends completely on mechanical placement of the visual image in the video space. An examination of white space around each character in the video space serves as a guide for alignment in yet another alignment technique. Moreover, an averaging technique can be used for alignment whereby one or more features (e.g., the baseline and edge) of the scanned image are selected and averaged. The averaged features are then used to align the scanned image in the video space.
The problem with all of the above-described alignment techniques is that errors for subsequent characters to be recognized are not predicted and adjustments are not made to the alignment apparatus to compensate for the errors. For example, the first scanned character may be positioned sufficiently correct in the video space for recognition. However, there may be a slight skew in the scanned line with respect to the line of travel of the scanner. As the scanner progresses over the line, the skew increases with each character that is scanned. With conventional alignment techniques, each character in this skewed line of characters has to be individually aligned. After a character is aligned and recognized, the process begins again for each subsequent character in the scanned line of characters. In the conventional alignment techniques discussed, no alignment information is carried over for subsequent character alignment. Consequently, time is lost in making the same alignment corrections as recognition progresses along the scanned line.
It is apparent that alignment in the horizontal direction is needed for each character, in addition to vertical alignment, when the pitch of the characters is not the same as the pitch of the box-like video space. The increased horizontal alignment adds to the time needed to align each character in the video space. Again, total recognition time will be increased because no alignment information from prior recognized characters is utilized to align and recognize remaining characters in a scan.